1. Field of the Invention
The present invention relates to a method for producing a hologram and a display device using the same. Particularly, it relates to a method for producing a screen hologram, and to a display device using the screen hologram.
2. Description of the Related Art
There is a known screen hologram which displays an image, which is output from a display unit, on a transparent screen which is made of the hologram, and an observer observes the image on the screen hologram by looking through from a rear side (background) of the screen.
As one example of use of the screen hologram, it is provided as a window of a bank or hospital so that it is possible to easily observe and meet with a customer or patient through the window. In this case, as the contents of the image, two kinds of images can be displayed, i.e., one is the image necessary for the customer or patient, and the other is the image necessary for an officer of the bank or hospital. Further, as another example of use, the screen hologram is provided as an advertising means in a showroom of a department store or shopping center in order to obtain a desirable advertising effect.
As mentioned above, since the screen hologram is widely utilized in various fields, the present invention aims to improve visibility of the hologram, particularly, the screen hologram when the observer observes the image displayed.
The primary object of the present invention is to provide a method for easily producing a hologram, for example, a screen hologram, having no cloudiness or cloudy state when an observer observes an image displayed on the screen.
The another object of the present invention is to provide a display device using the above hologram screen.
In accordance with one aspect of the present invention, there is provided a method for producing a hologram recording an interference fringe formed by an object light and a reference light on a photosensitive dry plate, and the object light either having diffusing and scattering characteristics or being passed through an optical diffusion body, including the steps of:
calculating a ratio xcex7R0/xcex700 of a first diffraction efficiency xcex700 and a second diffraction efficiency xcex7R0, the first diffraction efficiency xcex700 being obtained by the interference fringe formed by two object lights, and the second diffraction efficiency xcex7R0 being obtained by the interference fringe formed by the object light and the reference light; and
adjusting an intensity E0 of the object light and the intensity ER of the reference light in such a way that the ratio xcex7R0/xcex700 is set to at least 10 and the first diffraction efficiency xcex7R0 does not exceed 5%.
In a preferred embodiment, the intensity of the object light is set out of the sensitive area of the photosensitive dry plate.
In another preferred embodiment, the intensity of the object light is set to the extent that the first diffraction efficiency xcex700 obtained by the interference fringe formed by two object lights does not exceed 2%.
In still another embodiment, a ratio n0/nR of a magnification nR of a lens for diverging the reference light and the magnification n0 of a lens for diverging the object light is set to 4 or more.
In still another embodiment, the optical diffusion body and the photosensitive dry plate are arranged apart each other more than a predetermined distance.
In still another embodiment, an attenuation material for an optical intensity is arranged in the light path of the object light.
In still another embodiment, a ratio ER/E0 of the intensity E0 of the object light and the intensity ER of the reference light is set to 5 or more.
In accordance with another aspect of the present invention, there is provided a method for producing a hologram recording an interference fringe formed by an object light (or which passes through an optical diffusion body) and a reference light on a photosensitive dry plate, including the steps of:
arranging a half transmission mirror close to the photosensitive dry plate so that the object light is reflected by the half transmission mirror and the reflected object light is irradiated onto the photosensitive dry plate;
arranging an optical diverging body close to a rear side of the half transmission mirror so that the reference light is transmitted through the optical diverging body and the half transmission mirror; and
obtaining the hologram recording the interference fringe formed by the object light and the reference light on the photosensitive dry plate.
In a preferred embodiment, an angle of the half-transmission mirror is changeable so that a plurality of interference fringes are recorded on the photosensitive dry plate by changing the angle for irradiating the object light onto the photosensitive dry plate.
In another preferred embodiment, the half-transmission mirror has two reflection surfaces each having a different reflection angle for the object light so that a plurality of interference fringes are simultaneously recorded on the photosensitive dry plate.
In still another preferred embodiment, a plurality of interference fringes are simultaneously recorded on the photosensitive dry plate by using a plurality of object lights each having a different irradiation angle and being formed by irradiating lights from different directions onto the optical diffusion body.
In accordance with still another aspect of the present invention, there is provided a display device using a hologram recording an interference fringe formed by an object light and a reference light on a photosensitive dry plate, including:
a display unit for generating a signal light including an image to be displayed;
a hologram screen formed by either a transmission or a reflection hologram and having directivity in order to diffract and transmit the signal light irradiated from a predetermined angle range xcex1 to an observer; and
a projecting unit for projecting the signal light onto the hologram screen;
wherein a reflection preventing material (having transparency in the transmission hologram) is arranged at a rear side of the hologram screen, and has a low reflection rate for an incident angle of a first noise light or a second noise light; the first noise light is generated from a direction opposite to the predetermined angle range xcex1 to the hologram screen, and diffracted therefrom and transmitted therethrough; and the second noise light is normally reflected by the reflection preventing material, and has the same direction as the predetermined angle range xcex1.
In accordance with still another preferred embodiment, there is provided a display device using a hologram recording an interference fringe formed by an object light and a reference light on a photosensitive dry plate, including:
a display unit for generating a signal light including an image to be displayed;
a hologram screen formed by either a reflection or a transmission hologram, having a high diffraction efficiency for a light linearly polarized to a predetermined direction, and having directivity in order to diffract the signal light irradiated from a predetermined angle range to an observer; and
a projecting unit for projecting the signal light onto the hologram screen;
wherein a polarization optical element is arranged at a front side of the hologram screen so that the hologram screen selectively transmits the linearly polarized light having the high diffraction efficiency by passing it through the polarization optical element.
In a preferred embodiment, the hologram screen has a high diffraction efficiency for the light linearly polarized to a predetermined direction, and the polarization optical element is arranged at a front of the hologram screen.
In another preferred embodiment, a light absorbing material is arranged around the hologram screen so as not to obstruct a light path of a normalized light which is irradiated onto and output from the hologram screen.
In still another preferred embodiment, the hologram screen is the transmission type, and the projecting unit has a reflecting optical element in order to project the signal light from a slanting upper direction or a slanting lower direction of the hologram screen, and all structural elements of the display device are contained within a box having the same dimensions as that of the hologram screen.
In still another preferred embodiment, the display unit has a liquid crystal device and a light source for irradiating the light from a predetermined direction to the liquid crystal device.
In accordance with still another preferred embodiment, there is provided a display device using a hologram and taking a picture of an observer who observes a display screen, including:
a display unit generating a signal light including an image to be displayed;
a transmission or reflection hologram screen including a diffusion board;
an image optical system for forming the image of the signal light on the hologram screen;
a camera viewing the observer from the rear side of the hologram screen, and taking the picture of the observer.
In a preferred embodiment, a line connecting a center portion of the camera and an eye of the observer approximately corresponds to a line connecting a center of an image forming portion on the hologram screen and an eye of the observer.